Like other NSAIDs, it works by inhibiting the synthesis of prostaglandins, which are fat-like molecules derived from arachidonic acid, which are involved in mediating inflammation (swelling), pain, and fever. It achieves this effect on prostaglandin synthesis by inhibiting cyclooxygenase, an enzyme that is present in various tissues of the body.

It was originally made and patented in 1961, by the research arm of Boots Company led by Stewart Adams and marketed as Brufen.[8] Ibuprofen is now available under a variety of trade names, with the most notable being Advil, Motrin, and Nurofen.[8][9][10][11][12] Its discovery was the result of research during the 1950s and 1960s to find a safer alternative to aspirin.[8][12] It was later marketed, in 1966, as a prescription drug in the United Kingdom, then the United States in 1974.[8][12] Later in 1983 and 1984, it became the first NSAID (other than aspirin) to be available over the counter (OTC) in these two countries.[8][12] It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.[13]

In Europe, Australia, and New Zealand, ibuprofen lysine (the lysine salt of ibuprofen, sometimes called "ibuprofen lysinate" even though the lysine is in cationic form) is licensed for treatment of the same conditions as ibuprofen. The lysine salt increases water solubility, allowing intravenous use, and is indicated for closure of a patent ductus arteriosus in premature infants weighing between 500 and 1,500 grams (1 and 3 lb), who are no more than 32 weeks gestational age when usual medical management (e.g., fluid restriction, diuretics, respiratory support, etc.) is not effective.[17]

Ibuprofen may be quantified in blood, plasma, or serum to demonstrate the presence of the drug in a person having experienced an anaphylactic reaction, confirm a diagnosis of poisoning in hospitalized patients, or assist in a medicolegal death investigation. A monograph relating ibuprofen plasma concentration, time since ingestion, and risk of developing renal toxicity in overdose patients has been published.[19]

According to the US Food and Drug Administration, "ibuprofen can interfere with the antiplatelet effect of low-dose aspirin, potentially rendering aspirin less effective when used for cardioprotection and stroke prevention." Allowing sufficient time between doses of ibuprofen and immediate-release (IR) aspirin can avoid this problem. The recommended elapsed time between a dose of ibuprofen and a dose of aspirin depends on which is taken first. It would be 30 minutes or more for ibuprofen taken after IR aspirin, and 8 hours or more for ibuprofen taken before IR aspirin. However, this timing cannot be recommended for enteric-coated aspirin. But, if ibuprofen is taken only occasionally without the recommended timing, the reduction of the cardioprotection and stroke prevention of a daily aspirin regimen is minimal.[29]

Correlation between severity of symptoms and measured ibuprofen plasma levels is weak. Toxic effects are unlikely at doses below 100 mg/kg, but can be severe above 400 mg/kg (around 150 tablets of 200-mg units for an average man);[32] however, large doses do not indicate the clinical course is likely to be lethal.[33] A precise lethal dose is difficult to determine, as it may vary with age, weight, and concomitant diseases of the individual person.

Therapy is largely symptomatic. In cases presenting early, gastric decontamination is recommended. This is achieved using activated charcoal; charcoal adsorbs the drug before it can enter the systemic circulation. Gastric lavage is now rarely used, but can be considered if the amount ingested is potentially life-threatening, and it can be performed within 60 minutes of ingestion. Emesis is not recommended.[34] The majority of ibuprofen ingestions produce only mild effects and the management of overdose is straightforward. Standard measures to maintain normal urine output should be instituted and renal function monitored.[32] Since ibuprofen has acidic properties and is also excreted in the urine, forced alkaline diuresis is theoretically beneficial. However, because ibuprofen is highly protein-bound in the blood, renal excretion of unchanged drug is minimal. Forced alkaline diuresis is, therefore, of limited benefit.[35] Symptomatic therapy for hypotension, gastrointestinal bleeding, acidosis, and renal toxicity may be indicated. On occasion, close monitoring in an intensive-care unit for several days is necessary. A patient who survives the acute intoxication usually experiences no late sequelae.

A Canadian study published in the Canadian Medical Association Journal of thousands of pregnant woman suggests those taking any type or amount of NSAIDs (including ibuprofen, diclofenac and naproxen) were 2.4 times more likely to miscarry than those not taking the drugs.[36] However, an Israeli study following thousands of women found no increased risk of miscarriage in the group of mothers using NSAIDs.[37]

The exact mechanism of action of ibuprofen is unknown. Ibuprofen is a nonselective inhibitor of cyclooxygenase, an enzyme involved in prostaglandin synthesis via the arachidonic acid pathway. Its pharmacological effects are believed to be due to inhibition of cyclooxygenase-2 (COX-2) which decreases the synthesis of prostaglandins involved in mediating inflammation, pain, fever, and swelling. Antipyretic effects may be due to action on the hypothalamus, resulting in an increased peripheral blood flow, vasodilation, and subsequent heat dissipation. Inhibition of COX-1 is thought to cause some of the side effects of ibuprofen including gastrointestinal ulceration. Ibuprofen is administered as a racemic mixture. The R-enantiomer undergoes extensive interconversion to the S-enantiomer in vivo. The S-enantiomer is believed to be the more pharmacologically active enantiomer.[38]

Like aspirin and indometacin, ibuprofen is a nonselective COX inhibitor, in that it inhibits two isoforms of cyclooxygenase, COX-1 and COX-2. The analgesic, antipyretic, and anti-inflammatory activity of NSAIDs appears to operate mainly through inhibition of COX-2, whereas inhibition of COX-1 would be responsible for unwanted effects on the gastrointestinal tract.[39] However, the role of the individual COX isoforms in the analgesic, anti-inflammatory, and gastric damage effects of NSAIDs is uncertain and different compounds cause different degrees of analgesia and gastric damage.[40]

It is an optically active compound with both S and R-isomers, of which the S (dextrorotatory) isomer is the more biologically active; this isomer has also been isolated and used medically (see dexibuprofen for details).[6]

Ibuprofen is produced industrially as a racemate. The compound, like other 2-arylpropionate derivatives (including ketoprofen, flurbiprofen, naproxen, etc.), does contain a chiral center in the α-position of the propionate moiety. So two enantiomers of ibuprofen occur, with the potential for different biological effects and metabolism for each enantiomer. Indeed, the (S)-(+)-ibuprofen (dexibuprofen) was found to be the active form both in vitro and in vivo.

It was logical, then, to consider the potential for improving the selectivity and potency of ibuprofen formulations by marketing ibuprofen as a single-enantiomer product (as occurs with naproxen, another NSAID). Further in vivo testing, however, revealed the existence of an isomerase (alpha-methylacyl-CoA racemase), which converted (R)-ibuprofen to the active (S)-enantiomer.[41][42][43]

Ibuprofen was made available under prescription in the United Kingdom in 1969, and in the United States in 1974.[44] In the years since, the good tolerability profile, along with extensive experience in the population, as well as in so-called phase-IV trials (postapproval studies), has resulted in the availability of ibuprofen OTC in pharmacies worldwide, as well as in supermarkets and other general retailers.[citation needed] Ibuprofen is its INN, BAN, AAN and USAN approved name. Advil is manufactured by Pfizer and has been on the market since 1984.

Ibuprofen is commonly available in the United States up to the FDA's 1984 dose limit OTC, rarely used higher by prescription.[45] In 2009, the first injectable formulation of ibuprofen was approved in the United States, under the trade name Caldolor.[46][47]

In the UK, ibuprofen lysine is marketed as express pain relief, tension headache relief, and more commonly, migraine relief medicine. Usually available in packing of 16 342-mg tablets, the pack is marketed OTC by most supermarkets and pharmacies as their own branded product including Asda, Tesco, and Superdrug.[48]

Ibuprofen is sometimes used for the treatment of acne, because of its anti-inflammatory properties and has been sold in Japan in topical form for adult acne.[49][50] As with other NSAIDs, ibuprofen may be useful in the treatment of severe orthostatic hypotension (low blood pressure when standing up).[51] In some studies, ibuprofen showed superior results compared to a placebo in the prevention of Alzheimer's disease, when given in low doses over a long time.[52][53]

Ibuprofen has been associated with a lower risk of Parkinson's disease, and may delay or prevent it. Aspirin, other NSAIDs, and paracetamol (acetaminophen) had no effect on the risk for Parkinson's.[54] In March 2011, researchers at Harvard Medical School announced in Neurology that ibuprofen had a neuroprotective effect against the risk of developing Parkinson's disease.[55][56][57] People regularly consuming ibuprofen were reported to have a 38% lower risk of developing Parkinson's disease, but no such effect was found for other pain relievers, such as aspirin and paracetamol. Use of ibuprofen to lower the risk of Parkinson's disease in the general population would not be problem-free, given the possibility of adverse effects on the urinary and digestive systems.[58]